Last, P.R., Séret, B. and Naylor, G.J.P. 2016. A new species of guitarfish, Rhinobatos borneensis sp. nov. with a redefinition of the family-level classification in the order Rhinopristiformes (Chondrichthyes: Batoidea). Zootaxa 4117(4): 451-475.

Taxonomic Notes:

Has been mistaken for Rhynchobatus djiddensis (Forsskael, 1775) and R. australiae Whitley, 1939.

Justification:
The Smoothnose Wedgefish occurs off river mouths and shallow bays and is taken by multiple artisanal and commercial fisheries throughout its range both as a target species and as bycatch. Flesh is sold for human consumption and the fins from large animals fetch exceptionally high prices, creating a significant incentive for bycatch to be retained.

Little is known about the population status of Smoothnose Wedgefish, because of its fragmented and poorly understood distribution. Given its susceptibility to capture by multiple fishing gear types, including trawl nets, gillnets and hooks and its high value fins, it is inferred that numbers have been locally reduced by generally unregulated fishing throughout its range. Local population depletion of rhynchobatids can be inferred from Indonesia where the target gillnet fishery fleet for rhinids and rhynchobatids has declined significantly, reportedly due to declining catch rates. Therefore, globally this species is considered Vulnerable A2bd+3bd+4bd due to the past and ongoing population reduction and continued very high level of exploitation. Habitat destruction may also pose a significant threat to this species throughout much of its range.

The Smoothnose Wedgefish is a wide-ranging species first described from India that was widely confused with the Western Indian Ocean R. djiddensis across its range from the Arabian Sea to the Western Pacific. The species needs to be taxonomically assessed from adequate samples from various parts of its range in order to accurately determine its distribution. Recent taxonomic study of Rhynchobatus species have resulted in improved understanding of the distribution of the Smoothnose Wedgefish and it is no longer considered to occur in East Africa and Australian waters (P. Last, CSIRO, pers. comm., 2015).

Due to heavy inshore gillnet fishing, the Smoothnose Wedgefish population has probably decreased in parts of India but its population status elsewhere is unclear. Globally, shark and ray landings have declined by at least 20% since 2003, but the Indo-Pacific is amongst the regions where this decline has been more severe (Dulvy et al. 2014). Catches of sharks and rays in Southeast Asia are very high but are declining and fishers are travelling much further from port in order to increase catches (Chen 1996). Net and trawl fisheries in Indonesia (especially the Java Sea) and elsewhere are very extensive and as a result, many shark and ray species are highly exploited and stocks of most species have declined by at least an order of magnitude (Blaber et al.2009). Batoids are heavily exploited (White and Dharmadi 2007) and datasets from as early as 1963–1972 show the considerable decline in batoids in the Gulf of Thailand (Pauly 1979). Trawl and gillnet fisheries are also moving further afield. For example, in Jakarta the gillnet fishery at Muara Baru travels to waters around Kalimantan due to the decline in local populations (W.T. White, unpubl. data). While species-specific data on long-term declines in elasmobranchs in the Southeast Asian region are lacking, declines of the Smoothnose Wedgefish in Southeast Asia and elsewhere in the Indo-West Pacific are inferred given the widespread historical and continuing declines of demersal fisheries in this region (Stobutzki et al. 2006). Furthermore, the extensive loss and degradation of habitats such as coastal mangroves are another key threat to coastal and inshore species; Southeast Asia has seen an estimated 30% reduction in mangrove area since 1980 (FAO 2007, Polidoro et al. 2010).

The Smoothnose Wedgefish has a coastal distribution throughout its range, generally occurring on or close to the seabed, inshore off river mouths and in shallow bays. Very little is known about the life history characteristics of this species, however, they grow to at least 147 cm total length (TL) and possibly to 200 cm TL and reproduce by lecithotrophic viviparity (Compagno and Last 1999). Further research on the biology and exploitation of this species is urgently required. A recent age and growth study of Australian rhynchobatids pooled all three species (R. australiae, R. laevis and R. palpebratus) due to the difficulties in accurate species identification in the field (White et al. 2014) (note that since R. laevis does not occur in Australian waters, this study would have consisted of samples of the other two species). Growth rate was estimated at k = 0.41 year-1 (based on a logistic growth function), though variability in growth with age is likely between the species (White et al. 2014). Maximum age of the Smoothnose Wedgefish is unknown. In the absence of information, the generation length is estimated at 7 years, based on similarity in size and growth rates to the Giant Shovelnose Ray (Glaucostegus typus)which has a generation length of 7 years (White et al. 2014).

The Smoothnose Wedgefish is subject to capture in a variety of fisheries throughout its range (Compagno and Last 1999, W. White, pers. comm.). It is fished heavily by gillnet fisheries, for example, in India. Due to its similarity in both habitat and habits with the White-spotted Guitarfish (R. australiae), it is probably also vulnerable to other gear types, including trawl nets and hooks. Elasmobranch fisheries throughout this species' range are generally unregulated (Chen 1996), catches are poorly recorded (Bonfil 1994) and finning is widespread. Given this species' use of semi-enclosed and nearshore habitats, habitat destruction and pollution are thought to pose a significant threat, particularly in Southeast Asia.

Further investigation into the taxonomy, population and range, biology and ecology of the Smoothnose Wedgefish is required. Recent catch data for this species across its range is required to assess to what extent the population decline is occurring. Improved species composition data from all fisheries that take shovelnose rays and guitarfish is necessary. Management measures for this species are either limited or none existent for this species across a large part of its range.